A weigh boat is a small, disposable laboratory container used with sensitive weighing instruments, such as an analytical balance. This vessel holds solid or liquid chemical substances during precise mass measurement. Made from lightweight, inert materials, its core purpose is to ensure the sample can be accurately measured and then safely transferred without affecting the final mass reading.
Primary Function in Mass Measurement
The primary role of the weigh boat is to protect the highly sensitive weighing pan of the balance, which is calibrated to measure mass down to the sub-milligram level. Placing a chemical directly on the pan risks contamination or corrosion, which can permanently damage the instrument’s expensive internal sensors. The weigh boat serves as a barrier, containing the sample entirely and preventing any powder or liquid from coming into contact with the balance surface.
The boat’s design aids containment, featuring a flat bottom for stability and slightly sloped sides. This shape ensures powdered or granular substances remain centralized and can be easily poured without spillage. The lightweight nature of the boat also minimizes the overall mass placed on the balance and facilitates the clean transfer of the measured substance, reducing sample loss.
Variations in Design and Material
Weigh boats are manufactured from several different materials, with the choice depending on the chemical properties of the substance being weighed. The most common varieties are made from polystyrene, a rigid plastic that is chemically inert to many common laboratory solids and liquids. These plastic boats are popular because they are inexpensive, disposable, and feature a smooth surface that helps minimize sample adherence.
Specialized materials address specific needs. For instance, anti-static polystyrene or glassine paper boats are used for substances that generate static electric charges, which can cause fine powders to scatter. Aluminum weigh boats are employed when the sample must be heated, dried, or combusted at high temperatures, offering excellent heat and chemical resistance. Shapes also vary, including diamond-shaped or hexagonal boats for stability, and “pour boats” with flexible spouts for controlled dispensing.
The Procedure for Accurate Weighing
The correct procedure for using a weigh boat begins with placing the empty vessel onto the balance pan and then engaging the “tare” function. Taring electronically resets the balance display to zero, effectively subtracting the mass of the empty boat from any subsequent measurement. This step ensures that the final reading represents only the mass of the chemical sample itself.
The chemical substance must be added to the boat using a spatula or pipette, ideally while the boat is briefly removed from the balance to prevent accidental spillage. The technique of “weighing by difference” is often employed: the boat and sample are weighed together, a portion is transferred, and the boat is re-weighed to determine the exact mass dispensed. To maintain accuracy, laboratory gloves or a Kimwipe should be used to handle the boat, as oils and moisture from bare skin can introduce measurable errors.